Chromium steel



Patented June 14, 1938 UNITED STATES CHROMIUM STEEL Russell Franks, Niagara Falls, N. Y., assignor, by

mesne assignments, to Union Carbide and Car- I bon Corporation, a corporation of New York No Drawing.

Claims.

This invention relates to ferritic chromium steels that possess great toughness and excellent resistance to corrosion and oxidation at elevated temperatures.

When nitrogen is introduced into the ferritic high-chromium steels a marked reduction in grain size and an increase in strength are obtained without loss of ductility. Nitrogen increases the toughness of these steels without m'seriously impairing their resistance to corrosion or oxidation at elevated temperatures. In order to obtain these results it is necessary that the nitrogen be distributed substantially uniformly throughout the steel, a condition that can readily be obtained by adding the element, in" the form of a chromium nitride or other suitable nitrides, to the molten steel. The marked effect of nitrogen in improving the characteristics of the high chromium steels is most pronounced in steels that contain between about 15% and 35% of chromium, and the nitrogen content should be at least 0.10% and preferably at least 0.15%.

The present invention comprises improving the toughness of the above-described high-nitrogen chromium steels by introducing relatively. small amounts of copper or nickel or mixtures thereof.

The effectiveness of additions of these metals is indicated in the following table of data obtained on fully annealed steels:

Application June 8, 1935, Serial No. 25,618

provement in physical characteristics is most marked in wrought steels of relatively low carbon content; but a useful improvementis obtained by applying the invention to castings produced from higher carbon chromium steels.

The high-nitrogen chromium steels possess-a considerable resistance to grain growth at elevated temperatures and additions of nickel or copper, together or separately, impart some additional resistance to the grain growth that takes place on heating at elevated temperatures.

The nitrogen-bearing steels of the invention may be welded readily by either oxyacetylene or electric processes, and welds of improved properties are obtainable.

Steels according to the invention contain about 12% to chromium, at least 0.10% and not over about 0.65% nitrogen, at carbon content no greater than 1%, and a content of nickel'or copper, or both, between about 0.25% and about-3%. If copper alone is used, it preferably does not exceed about 2.5% of the steel. If the steel is to be wrought, the carbon content is preferably below about 0.3%. The nitrogen should be distributed substantially uniformly throughout the steel and preferably exceeds 0.15%. The customary fractional percentages of silicon and manganese required to produce steel of good quality are, of course, preferably added.

Tensile tests 'Anal Yield Max. er- Per- Izod 35 point stress cent cent impact,

Per- Per- Per- Ier- Perpounds] pounds/ el. in red. of footeent cent cent cent cent sq. in. sq. in 2 in. area pounds Gr 0 N; On I Ni 22.30 0.10 0.25 None None 54.000 85,000 32 66 18 22.78 .09 .20 0.53 None 53,000 88,500 20 56 30 22.60 .00 .20 2.18 None 57,000 89,000 27 56 37 22.27 .12 .28 None 1.20 07,000 124,000 23 47 36 25.86 .12 .30 None None 54,000 85,500 30 00 14 25.1 .10 .29 None 1.60 62,000 94,000 25 50 37 It is shown by this table of data that when I claim:

small amounts of copper or nickel are introduced into ferritic chromium steels containing nitrogen, there is obtained an appreciable improvement in toughness as measured by the Izod impact test, in fact, far more toughness than one would expect to obtain by the addition of such relatively small percentages of either element. Furthermore, the other valuable physical characteristics of the nitrogen-bearing steels, such as resistance to heat and corrosion, are retained. The im- 1. Alloy steel having in the fully annealed state an impact strength at least 30 foot pounds Izod, .and containing about 22% to 35% chromium, carbon in amounts not exceeding 1%, at least 0.1% and not over 0.65% nitrogen distributed substantially uniformly throughout the steel, and at least 0.25% but not over 3% metal selected from the group consisting of nickel, copper, and mixtures of nickel and copper; the remainder being substantially all iron.

2. Alloy steel having in the fully annealed state an impact strength at least 30 foot pounds Izod, and containing about 22% to 35% chromium, carbon in amounts not exceeding 1%, at least 0.1% and not over 0.65% nitrogen distributed substantially uniformly throughout the steel, and at least 0.25% but not over 3% nickel, the remainder being substantially all iron.

3. Alloy steel having in the fully annealed state an impact strength at least 30 foot pounds Izod, and containing about 22% to 35% chromium, carbon in amounts not exceeding 1%, at least 0.1% and not over 0.65% nitrogen distributed substantially uniformly throughout the steel, and at least 0.25%-but not over 2.5% copper, the remainder being substantially all iron.

4. A wrought article of alloy steel having in the fully annealed state an impact strength of least 30 foot pounds Izod, and containing about 10 22% to 35% chromium, carbon in amounts up to about 0.3%, at least 0.15% andv not over 0.65% nitrogen distributed substantially uniformly throughout the steel, and at least 0.25% but not over;2.5% copper; the remainder being substanl5 tially all iron.

RUSSELL FRANKS. 

